5

LTC1734

BLOCK DIAGRA

–

+

–

+

–

+

2

5

UVLO

VOLTAGE

REFERENCE

2.5V

SHUTDOWN

SHUTDOWN

SHUTDOWN

SHUTDOWN

GND

1734 BD

4

PROG

2.5V

10

µF

A1

A2

A3

1.5V

–

+

C1

2.15V

3

µA

BAT

SINGLE

Li-Ion

CELL

6

DRIVE

1

1

µF

TEMPERATURE AND

CURRENT LIMITING

60

Ω

0.06

Ω

3

REF

OUTPUT

DRIVER

external PNP emitter. The PNP collector provides charge

current to the battery.

GND (Pin 2): Ground. Provides a reference for the internal

voltage regulator and a return for all internal circuits.

When in the constant voltage mode, the LTC1734 will

precisely regulate the voltage between the BAT and GND

pins. The battery ground should connect close to the GND

pin to avoid voltage drop errors.

supplies power to the internal control circuitry and exter-

nal PNP transistor through the internal current sense

resistor. This pin should be bypassed to ground with a

capacitor in the range of 1

µF to 10µF.

PROG (Pin 4): Charge Current Programming, Charge

Current Monitor and Manual Shutdown Pin. Provides a

virtual reference voltage of 1.5V for an external resistor

the battery charge current when the charger is in the

constant current mode. The typical charge current will be

1000 times greater than the current through this resistor

current to be monitored. The voltage on this pin is propor-

tional to the charge current where 1.5V corresponds to the

full programmed currrent. Floating this pin allows an

internal current source to pull the pin voltage above the

shutdown threshold voltage. Because this pin is in a signal

path, excessive capacitive loading can cause AC instabil-

ity. See the Applications Information section for more

details.

BAT (Pin 5): Battery Voltage Sense Input. A precision

internal resistor divider sets the final float voltage on this

pin. This divider is disconnected in the manual shutdown

or sleep mode. When charging, approximately 34

µA

flows into the BAT pin. To minimize float voltage errors,

avoid excessive resistance between the battery and the

BAT pin. For dynamically stable operation, this pin usually

requires a minimum bypass capacitance to ground of 5

µF

to frequency compensate for the high frequency inductive

effects of the battery and wiring.

DRIVE (Pin 6): Base Drive Output for the External PNP

Pass Transistor. Provides a controlled sink current that

drives the base of the PNP. This pin has current limiting

protection for the LTC1734.